This invention relates to headwall structures and in particular to improved lightweight headwall structures used with standard culvert or drainage pipes in infrastructure water management system. Because they are lightweight while having adequate strength, headwall structures according to the invention are easily transported and installed. They may be largely prefabricated. They are intended to be used in substitution for standard heavy concrete headwalls.
Headwalls are structures that attach to the end of a culvert or drainage pipe and support the surrounding earth or fill, thus preventing or impeding local erosion and undercutting of the bank around the culvert, thereby minimising the risk of serious washout. These structures also facilitate the attachment of auxiliary components, e.g., trash gates for debris and animal control, security grids for prevention of entry into culvert or pipe, weir boards for use in control of water flow and levels in agricultural installations, etc. Such structures include a back wall having an orifice to receive a culvert or pipe, and often include a tray joined to the lower edge of the back wall and extending outwards therefrom and may have two outwardly flared (diverging) wings or sidewalls joined to the back wall and to the tray to retain and stabilize the surrounding earth or fill side wings for earth bank stabilization. The wings and tray when present as part of a headwall structure used as an outflow (exit) structure downstream of the culvert or pipe, direct the outflow received from the pipe or culvert away from the headwall. If used as entrance structures upstream of the pipe, such headwall structures receive water from a source such as an open ditch or drain and direct the water into the orifice and thence into a connected pipe if such is present.
Conventionally such headwall structures are made of relatively heavy concrete either formed in place or precast. It is well known that structures formed in place are labour-intensive and may also require prolonged traffic diversion if they have to be erected in association with a road in use. Because of their heavy weight, precast concrete structures require heavy-duty equipment to transport, handle and install. Additionally, concrete has several disadvantages. It is rigid and prone to cracking in the event of earth movement due to seismic events or subsidence or due to permafrost conditions in northern areas. Concrete is not environmentally friendly due to leaching of material into the ground water. It is also highly porous and subject to spalling and salt absorption.
A representative conventional culvert with associated concrete headwall can be found in U.S. Pat. No. 4,993,872 to Lockwood; this patent discloses a prefabricated headwall but without a pipe. A concrete headwall for use with a connected pipe is disclosed in U.S. Patent No. 3,779,021 to Green. An alternative concrete structure for connection to a pipe is disclosed in U.S. Pat. No. 5,551,798 to Goodreau. On occasion the use of plastics materials for coupling pipe to another structure has been proposed; see for example U.S. Pat. No. 5,971,663 to Brothers.
The Green patent discloses headwalls manufactured by pouring concrete into a light plastic prefabricated form. This method substantially reduces the amount of labour required to build the headwall, but still requires considerable time and effort, because the concrete has to be transported to the site. Poured-in-place concrete is increasingly unacceptable because of potential negative environmental and ecological impact on wildlife habitats and drinking water quality. Note that the Green design, because of the complexity of surface detail, would not readily accommodate after-market add-on auxiliary devices such as trash gates, security grids and weir boards.
Goodreau""s disclosed structure embodies two prefabricated end walls of the culvert with a specific retainer system; his structure suffers from the inherent disadvantages of using concrete slabs. Goodreau does not disclose the use of sidewalls or wings that retain the adjacent earth bank, so there could be a tendency for the earth bank to spill over the flat bottom portion of the headwall outlet area. Goodreau""s design does not retain side bank slope material nor minimize ingress into pipe opening, nor does it provide complete retention of the integrity of the side slope. His headwall may not be suitable for permafrost or boggy areas without some modification, because his footings appear to be inadequate for the weight of the precast concrete unit. The structural stability of the Goodreau design is reliant on the stability of the backfill material, as no other means of supporting the headwalls to remain vertical is apparent other than the pipe connection itself.
Other patents disclosing prefabricated concrete headwall structures, mostly for use with box culvert systems or other channel constructions, include U.S. Pat. Nos. 2,041,267 to Schroeder, and 5,836,717 to Bernini.
An inexpensive headwall constructed from material other than concrete was proposed in U.S. Pat. No. 4,723,871 by Roscoe. This headwall for culverts consists of a substantially monolithic plastics shell structure, filled with a granular material or a flowable material capable of solidifying. This specific headwall is simpler and lighter than many known before it; however, it does not provide reliable performance in use. Roscoe""s design does not offer full bank retention nor prevent undermining of the structure from water flow, as it does not provide wing walls nor an extended base. Further, Roscoe""s design does not permit rapid installation under adverse weather conditions; yet once installed, it cannot be readily removed if need be. The manufacture in place of the Roscoe structure may not be economically viable in remote areas nor environmentally acceptable in maintaining non-contamination of water systems from poured-in-place materials during installation.
In short, while various previously known designs have utility, they all suffer from disadvantages. A strong, reliable, lightweight, easily transported and easily installed structure is needed that will provide adequate bank stabilization and adequate downstream water diversion away from the surrounding earth or fill. Such structure should be readily connectable to associated pipe and should be readily capable of receiving auxiliary devices such as trash gates, security grids and weir boards for attachment thereto. A problem to overcome is that while reinforced concrete structures are sufficiently heavy to tend to stay in place and sufficiently strong and rigid to maintain structural stability under load, a lightweight unit designed to serve the same purpose as a given concrete headwall may lack inherent structural stability and may not readily withstand the forces imparted to it in use.
A principal object of the present invention is to provide a headwall structure that meets the foregoing need and overcomes the disadvantages of conventional headwalls. Such structure should facilitate the control of water flow, erosion, flooding, silt and debris and should be readily attachable to any culvert pipe of any type, size or style, used in an infrastructure water management system.
Another object of the present invention is to provide a headwall that is economical, efficient, easy to install, and also easy to remove to accommodate the possibility of future reclamation of areas to their natural state.
Another object of the present invention is to provide a headwall structure with earth-stabilizing sidewalls and a bottom plate or tray providing in combination with the sidewall configuration (including associated reinforcing elements preferably integrally formed therewith) a suitable water flow channel that serves either as an outlet chute defining a satisfactory exit channel configuration for water outflow, or when used in reverse (entrance) orientation, a satisfactory inlet flow channel configuration.
Yet another object of the present invention is to provide a headwall of relatively light weight and therefore relatively well suited for use in areas subject to permafrost or high-water-table areas as compared with conventional concrete structures.
Such headwall should be suitable for use in many different types of terrain, possibly even in some areas of unstable ground. Such structure should provide good earth or fill anchorage in fast-flow situations.
In accordance with the foregoing objectives, one preferred embodiment of a headwall according to the invention is formed as an integral prefabricated structure preferably using a composite of plastics material and glass fibers, and preferably incorporating selected cores of selected core material in selected portions of the structure, especially where additional mass, rigidity or strength is requiredxe2x80x94typically in those portions of the structure that may be expected to be under load. Instead of steel bar reinforcement that is conventional in the manufacture of precast reinforced concrete, different cores of different materials can be used, depending upon the situation. One option is to use a polymer concrete core material that is reinforced by incorporating a composite laminate fully encapsulating the polymer concrete and that can be incorporated selectively to form a relatively rigid skeleton or framework that supports the composite laminate material overlying the polymer concrete.
While a preferred headwall structure according to the invention is preferably formed as an integral unit, such structure may be thought of as comprising a number of interconnected members including a generally vertical back wall optionally incorporating a pipe-receiving orifice, a tray joined to the lower edge of the back wall and extending generally horizontally outwardly therefrom, and a pair of sidewalls on either side of and joining both the back wall and the outlet tray. The tray may be a generally planar continuum or may be stepped downwardly outwardly or otherwise shaped to meet the inflow or outflow requirements to be met for any particular installation. The top edge of the back wall, the top and outer edges of the sidewalls, and the outer edge of the tray are each preferably provided with margins that provide a degree of rigidity to the integral structure and additionally serve to stabilize earth or fill in the immediate vicinity of the headwall. The aforementioned elements are preferably prefabricated as a single integral structural unit.
The sidewalls may be generally planar or may be curved, in the manner described below. Equally, the upper edges and associated margins of the sidewalls may be generally rectilinear, but may instead be generally convex. The use of curved surfaces tends to strengthen the resulting structure.
In headwalls according to the invention, the thickness of the laminate can be varied and the type or quantity of composite reinforcement can be varied so as to vary the overall physical properties of the structure. Suitable adjustment of mass and quantity and type of reinforcement can accommodate the varying structural requirements of headwalls of varying sizes. In contrast with conventional precast concrete designs, the required structural rigidity of headwalls according to the invention is provided primarily by form and bracing rather than by thickness and weight.
To provide walls of a given strength, composite laminates can be formed as relatively thin, lightweight panel sections whose outermost edges may continue as flanged margins for both rigidity and earth retention. A problem with such relatively thin-walled material, however, is that the walls can easily flex under load, and a headwall made of such material will lack inherent mass and thus be susceptible to shifting once installed in an earth bank or the like. According to an aspect of the invention, at least the lower outer portions of the sidewalls are sculpted to provide both structural reinforcement and stabilizing cavities or recesses into which earth or fill enters upon installation to help stabilize the structure. In one embodiment of the invention, the sidewalls comprise wing panels diverging from one another, the rear vertical edges of the wings being common with the vertical side edges of the backwall, and reinforcing panels interconnecting the wings to outer side portions of the tray and to the lower side margins of the sidewalls. The reinforcing panels are at an oblique angle to both the wings and to the tray so as to provide a buttressing reinforcement for the wings. The back wall, tray, sidewalls (including both wings and reinforcing panels) and margins form a single continuous surface defining the flow channel for constraining the water flow.
Reinforcing panels designed as aforesaid perforce provide cavities or recesses at the outsides of the lower outer portions of the sidewalls, permitting earth or fill to enter into and bear against the outer surfaces of the reinforcing panels defining these recesses, thereby helping to stabilize the structure in the earth bank or the like in which it is installed. Such stabilization function is enhanced if the recesses are partially closed off in the outer portion thereof by front reinforcing panels lying in a plane that will be close to parallel to the slope of the earth or fill in the vicinity and also close to perpendicular to the water flow. These front reinforcing panels tend to prevent or impede earth or fill from moving outwards in the vicinity of the lower side edges of the sidewalls, as well as providing stiffness and buttressing reinforcement for the adjoining portions of the sidewalls. If desired, backfill may partly cover the outer front surfaces of the front reinforcing panels to help anchor the structure. For use in entrance mode, the front reinforcing panels are preferably inwardly inclined so as to direct water into the entrance channel of the headwall structure.
Alternatively, as much of the foregoing structure as wished may be formed as a curved continuum. Instead of discrete planar panels, albeit integrally formed together as a single unit, the wings, top brace above the back wall, reinforcing panels, and even at least the side portions of the back wall itself, may be integrally formed as a curved continuum. In such curved continuum embodiment, the lower outer edges of the sidewalls should be reverse-curved to provide convex surfaces relative to the interior flow channel space defined by the sidewalls and the tray, for preferred flow channel definition and so as to stiffen and buttress the upper portion of the sidewalls. These convex surfaces are of course concave on the outside surfaces of the sidewalls and form recesses or cavities engaged by the adjacent soil bank. As in the case of the planar panel embodiment earlier described, the lower outer portions of the reverse-curved surfaces should include a substantial front surface area that lies generally parallel to the slope of the adjacent earth bank so as to define with the remaining concave surfaces of the reverse-curved portions of the sidewalls a substantial recess or cavity that receives a substantial amount of earth or fill and thus helps to stabilize the headwall structure in place, and which front surface area can be partially covered by backfill if desired.
Hybrids of the foregoing designs are possible; for example the back wall and tray may be generally planar, the sidewall wings curved, the reinforcing panels either planar or curved but not following the curvature of the wings.
In this description, terms such as xe2x80x9cverticalxe2x80x9d and xe2x80x9coutwardxe2x80x9d are relative and apply to the installed headwall. Further, as the overall orientation of any given headwall as installed will be variable, and as the demands of any particular culvert outlet (say) will be variable, some latitude is to be given such terms. For example, if the headwall is located at the top of a sloped land area, it may be desired that the tray, serving as an outlet tray, also be designed to be downwardly outwardly sloped so as to merge with the land, rather than having a strictly horizontal orientation, or its margin extended as an apron to impede erosion of the earth bank thereunder. Note also that as a given headwall may be installed either upstream or downstream of a culvert (say) for use either as an exit structure or an entrance structure, the terms xe2x80x9cupstreamxe2x80x9d and xe2x80x9cdownstreamxe2x80x9d, xe2x80x9coutflowxe2x80x9d, and the like, are inherently relative. For convenience of description, an exit mode of use of the headwall is frequently presumed in this specification unless otherwise specified; a term such as xe2x80x9coutlet trayxe2x80x9d used to describe an element of the headwall is used in such relative sense. Clearly if the headwall were reversed in orientation for use in entrance mode immediately upstream of a culvert inlet, the tray of the headwall structure would in fact serve as an inlet tray. The term xe2x80x9clongitudinalxe2x80x9d herein refers to the general direction of water flow and is coincident with the axis of the pipe stub or spigot to be described below.
The sidewall structure preferably comprises a pair of side brace panels, one for each said sidewall. Each side brace panel may conveniently extend obliquely between (and relative to) both the associated sidewall wing and a respective side portion of the tray. Each side brace panel is fixed along an upper edge to the associated sidewall wing and along a lower edge to the tray. The side brace panel may be formed integrally with and as an angled continuum of the associated sidewall wing, and likewise may form a continuum with the tray. For surface continuity, earth bank stabilization and further reinforcement of the sidewall structure, a pair of generally triangular front brace panels join the outer edges of the side brace panels to the outward portion of the tray and to the front side margins. The outer bottom edge of each front brace panel may stop short of the outer edge of the tray and may be angled inwardly so that if the headwall is installed for entrance use (so that the tray becomes an inlet tray), water will be directed inwardly for channeling into the entrance channel. The combined exposed surfaces of the brace elements and the tray serve to define chute (flow channel) surfaces for either incoming or effluent water, depending upon the installation, in either case providing a preferred flow channel shape for the water flow. The brace elements further provide buttressing of the wings. The brace elements further define the cavity or recess earlier described at the outer lower side edges of the sidewalls for receiving earth or fill to help stabilize the structure.
Where the curved continuum embodiment of the invention or a hybrid embodiment is designed and used, the front brace panels may be planar and the side brace panels curved, or both sets of panels may be curved, or there may be no discrete side or brace panels, but simply a continuous curved surface, the outer lower portion of which is reverse-curved as previously described to provide a convex inside surface for preferred chute configuration and a concave outside surface for stabilizing the structure in the earth bank or the like.
All of the constituent walls of this structure may conveniently be of substantially uniform cross-section whereby the front and rear surfaces of the headwall structure are substantially identical. The flanged margins optionally but preferably provided along the back wall and sidewalls of the structure and formed at a substantial angle to the adjoining walls further reinforce the structure and facilitate stabilization of the adjacent earth bank.
Note that headwall structural units as described may be configured to nest and stack, and therefore can be economically shipped in large quantities.
Advantageously, for connection to a pipe, the headwall is provided with a spigot mating with the pipe or with a range of possible pipe connections. It is advantageous that the spigot be designed for maximum adaptability. To this end, the spigot may be formed to be substantially dimensionally identical to a section of a standard pipe so that a connector for such pipe will fit the spigot without the requirement of any special adapter. Thus a given manufacturer""s pipe section can be connected to the headwall structure as desired. The prefabrication permits the spigot to be designed to mate with the pipe connection system of any given pipe manufacturer.
To build a spigot that conforms to a given pipe connection system, the headwall manufacturer may advantageously use an actual pipe section having a terminal end portion structured in conformity with a given manufacturer""s specifications, and may, using an appropriate mold, replicate this end portion exactly on the spigot, thereby to generate a spigot of a particular size and form that can be interconnected with a mating pipe section by using the manufacturer""s double female coupling element. To this end, a section of the terminating portion of the actual pipe is inserted into a hollow container from which a female mold is prepared. The spigot mold can then be integrated with other mold portions to form part of the overall mold for the headwall, and is used to generate a spigot inherently configured in exactly the same pipe-end configuration as the mating pipe to which the spigot is designed to be coupled. Such spigot design facilitates a bond generally free of leaks, a smooth confluence of interior surfaces, and without loss of cross-sectional area within the headwall. Such design also facilitates and expedites installation.
Some but not all of the advantages of the above-described embodiments of the invention can be obtained by manufacturing the headwall structure as a set of discrete substructures that are finally assembled together on site. For example, the tray and associated margin could be one substructure, each of the sidewalls with margins another substructure, and the back wall, top cross-piece margin and spigot a further substructure. These substructures could be provided with fasteners for mechanical interconnection, or could be bonded together by laminating or adhesive bonding or the like. This manufacturing approach may be desirable where the fully assembled headwall structure is very large or very heavy.
Further, since the manufacturer of headwalls according to the invention will probably wish to provide headwalls having differently configured spigots that match terminating ends of various pipe connection systems, it is advantageous to manufacture the spigot units as discrete components, each having a standard interface for mating with another component of the complete headwall structure. The manufacture and sale of headwalls as such two-component structures can help reduce the size and weight of the manufacturer""s inventory. In such two-component headwall structures, one component is the spigot that is molded integrally with an immediately adjoining flanged wall structure (open, of course, with the same interior opening as the spigot itself). The other component, comprising the main body portion of the headwall, is provided with a mating aperture in its back wall for receiving the flanged wall of the spigot portion in a mating engagement. The interface between the spigot component and the body component is accordingly standard, so that a number of different spigot components for connection to a number of different standard pipes could be available in manufacturer""s inventory, each mating with the body portion of the headwall by reason of the mating of the outer periphery of the spigot flange with the aperture of the body portion of the headwall. A square interface is preferred for ease of manufacture and because one need not be concerned about the orientation of the spigot component when fitting it to the aperture in the body portion of the headwall.
The spigot component can be both chemically bonded and mechanically fastened within the aperture of the body component using any glues and fasteners desired (e.g., plastics bonding glue, screws or various nut-and-bolt arrangements, or attachment brackets) once the outer surfaces of both components are flush.
This two-component design permits the manufacturer to have available in inventory a relatively small number of precast body portion components and few if any spigot components; the manufacturer may cast spigot components on demand as orders come in. The total volume and weight of the manufacturer""s inventory can thus be appreciably reduced. Further, the shipping weight of each component and the size of each component is lower than if the two were combined into an integral unit, and handling each individual component is facilitated. A disadvantage of these two-component headwall structures is that fasteners and an assembly operation are required, presumably on site, to couple the two components of the headwall together. This disadvantage, however, is expected for most installations to be more than offset by the aforementioned advantages.
Headwall structures made according to the invention are relatively environmentally safe, because the structures can be made of materials not subjected to serious erosion or leaching, and may be suitably coated to this end. All materials used to fabricate these structures can be selected to be chemically resistant to acids and alkalis, including road salts and wood preservatives. Such inert materials are not conducive to bacterial growth.
The gross weight of a headwall structure according to the invention can be as little as 10 to 15 percent of the weight of a conventional precast concrete structure suitable for use in the same location. It can be readily seen that the use of headwall structures according to the invention can substantially reduce the cost of labour, handling, shipping, and lifting equipment for installation of such structures as compared with the cost of conventional structures.